Just been making a display board for a few Command bits. I found a BC-450-A 3 dial rx tuning unit. On it, in yellow, it says "6V AC R-31 Tested" What's an R-31? I also found a C-43 ARC-5 tuning box, but it only has 2 tuning dials but three sets of connectors and mode/gain switches.? Why ?? Ben. www.militarywirelessmuseum.co.uk